Microcomputer

ABSTRACT

A built-in memory is divided into the following two types: first memories  5  and  7  and second memories  4  and  6 , and made accessible in parallel by third buses XAB and XDB and second buses YAB and YDB respectively. Thereby, a CPU core  2  can simultaneously transfer two data values from the built-in memory to a DSP engine  3 . Moreover, the third buses XAB and XDB and the second buses YAB and YDB are also separate from first buses IAB and IDB to be externally interfaced and the CPU core  2  can access an external memory in parallel with the access to the second memories  4  and  6  and the first memories  5  and  7.

This application is a continuation of application Ser. No. 08/630,320filed on Apr. 10, 1996, now U.S. Pat. No. 5,867,726.

BACKGROUND OF THE INVENTION

The present invention relates to a logic semiconductor integratedcircuit (LSI) provided with a central processing unit (CPU) and adigital signal processing unit (DSP) and formed into a semiconductorintegrated circuit and an art effectively applied to a data processor(e.g. single-chip microprocessor or single-chip microcomputer) forhigh-speed processing.

Japanese Patent Application No. 296778/1992 (corresponding to U.S. Pat.No. 08/145157, filed Nov. 3, 1993, now abandoned) is a documentdescribing a single-chip microcomputer in which an arithmetic and logicunit and a multiplier are mounted on the same semiconductor chip.

According to the above invention, a logic LSI chip includes a centralprocessing unit, a bus, a memory, and a multiplier and particularly hasa command signal line for transferring a command for a multiplicationinstruction related to read data from the central processing unit to themultiplier while reading the data out of the memory. As a result,because the command of the multiplication instruction related to readdata is transferred from the central processing unit to the multiplierwhile the central processing unit reads data out of the memory, it ispossible to directly transfer data between the memory and themultiplier.

SUMMARY OF THE INVENTION

The present inventor and others studied formation of a centralprocessing unit and a digital signal processing unit (DSP) in asemiconductor integrated circuit (LSI) and acceleration of digitalsignal processing.

The above document realizes acceleration of multiplication by making itpossible to directly transfer data from a memory to a multiplier.However, when assuming pipeline processing of instruction execution by acentral processing unit, the above document does not consider thesituation in which the fetch cycle of an instruction to be executed by acentral processing unit competes with the memory access cycle formultiplication.

Moreover, the above document does not consider reading a plurality ofoperands for addition and multiplication out of a memory in parallel andaccelerating operational processing. Furthermore, in this case, it isfound by the present inventor and others that the operational easinessof a microcomputer is deteriorated unless considering the relation withexternal access by the central processing unit.

Furthermore, it is found by the present inventor and others thatdevising the assignment of codes to a CPU instruction (firstinstruction) and a DSP instruction (second instruction) and the formatof the DSP instruction are also necessary to restrain the increase ofthe logic scale of an instruction decode circuit to the utmost.

It is an object of the present invention to accelerate digital signalprocessing by mounting a central processing unit and a digital signalprocessing unit on one semiconductor integrated circuit.

It is another object of the present invention to restrain the increaseof the physical scale of a semiconductor integrated circuit whenmounting a central processing unit and a digital signal processing uniton the semiconductor integrated circuit.

It is still another object of the present invention to-provide a dataprocessor whose operational easiness is improved and which includes acentral processing unit and a digital processing unit on the samesemiconductor chip.

It is still another object of the present invention to provide a dataprocessor in which digital signal processing is accelerated.

It is still another object of the present invention to provide aninstruction format (instruction set) preferably applied to a dataprocessor including a central processing unit and a digital signalprocessing unit in the same semiconductor chip.

It is still another object of the present invention to provide aninstruction format (instruction set) capable of restraining the increaseof the logic scale of an instruction decode circuit in a data processorincluding a central processing unit and a digital signal processing unitin the same semiconductor chip.

The above and other objects and novel features of the present inventionwill become apparent from the description of this specification and theaccompanying drawings.

A typical embodiment of the invention disclosed in this application isbriefly described below.

That is, a semiconductor integrated circuit (microcomputer) comprises asemiconductor chip including:

a central processing unit (2);

first to third address buses (IAB, YAB, and XAB) to which an address isselectively transferred from the central processing unit;

first memories (5 and 7) connected to the first address bus (IAB) andthe second address bus (YAB) and to be accessed by an address sent fromthe central processing unit;

second memories (4 and 6) connected to the first address bus (IAB) andthe third address bus (XAB) and to be accessed by an address sent fromthe central processing unit;

a first data bus (IDB) for transferring data, which is connected to thefirst and second memories and the central processing unit;

a second data bus (YDB) for transferring data, which is connected to thefirst memories;

a third data bus (XDB) for transferring data, which is connected to thesecond memories;

an external interface circuit (12) connected to the first address busand the first data bus;

a digital signal processing unit (3) connected to the first to thirddata buses and synchronously operated by the central processing unit;and

a control signal line for transferring a DSP control signal (20) forcontrolling the operation of the digital signal processing unit from thecentral processing unit to the digital signal processing unit.

According to the above means, a built-in or an internal memory isdivided into the following two types by considering multiply andaccumulate operation: first memories (5 and 7) and second memories (4and 6). Then, the central processing unit (2) is made possible to accessthe first and second memories by the third internal buses (XAB and XDB)and the second internal buses (YAB and YDB) in parallel. Thereby, it ispossible to transfer two data values to the digital signal processingunit from the built-in memory at the same time.

Moreover, because the third internal buses (XAB and XDB) and the secondinternal buses (YAB and YDB) are also separated from the first internalbuses (IAB and IDB) to be interfaced with an external unit, the centralprocessing unit can access an external memory in parallel with theaccess to the second memories (4 and 6) and the first memories (5 and 7)by using the first internal buses (IAB and IDB).

Thus, because the data processor of the present invention has threeinternal address buses (IAB, XAB, and YAB) and three internal data buses(IDB, XDB, and YDB) in the first to third internal buses connected tothe central processing unit (2), the processor can access differentmemories at the same clock cycle by using the first to third internalbuses. Therefore, even if a program or data is present in an externalmemory, the data processor of the present invention can easilyaccelerate arithmetic processing.

To improve the operational easiness of a microcomputer, the first andsecond memories are preferably are RAM and ROM, respectively.

To accelerate generation of addresses for repetition of the multiply andaccumulate operation in the central processing unit, it is preferable toprovide a modulo address output portion (200) for the central processingunit. In this case, it is preferable that an address generated by themodulo address output portion can selectively be output to the second orthird address bus.

The digital signal processing unit includes first to third data buffermeans (MDBI, MDBY, and MDBX) to be individually interfaced with thefirst to third data buses (IDB, YDB, and XDB), a plurality of registermeans (305 to 308) being made connectable to each data buffer meansthrough an internal bus, a multiplier (304) and an arithmetic and logicoperation unit (302) connected to the internal bus, and a decoder (34)for decoding the DSP control signal and controlling operations of thedata buffer means, multiplier, arithmetic and logic operation unit, andregister means.

For instruction decoding, a data processor (microcomputer) is formedinto a single semiconductor integrated circuit chip including thecentral processing unit (2), the memories (4 to 7) to be accessed andcontrolled by the central processing unit, a data bus for transferringdata between the memories and the central processing unit, and thedigital signal processing unit (3).

An instruction set executable by the microcomputer includes a CPUinstruction (first instruction) to be executed by the central processingunit (2) and a DSP instruction to be executed by the digital signalprocessing unit (3) by making the central processing unit perform sometypes of processing including address computation for data fetch.

The central processing unit includes an instruction register (25) forfetching a 16-bit fixed-length (first bit length) CPU instruction and a16-bit or 32-bit (second bit length) DSP instruction through the databus and a decoder (24) for discriminating the CPU instruction from theDSP instruction in accordance with a plurality of bits of some of thecommands fetched by the instruction register and generating a DSPcontrol signal (20) for controlling operations of the digital signalprocessing unit and a CPU control signal for controlling operations ofthe central processing unit in accordance with the discriminationresult.

For example, a CPU instruction is assigned to a range in which the 4high-order bits of an instruction code are set to “0000” to “1110”. ADSP instruction is assigned to a range in which 4 high-order bits of aninstruction code are set to “1111”. Moreover, 6 high-order bits of aninstruction code are used as a “111100” instruction code. An instructionin which 6 high-order bits of an instruction code are set to “111110” isused as a 32-bit instruction code. However, no instruction is assignedto a range in which 6 high-order bits of an instruction code are set to“111111” and the range is used as a vacancy.

Thus, by providing the above rule for assignment of codes to up to32-bit instructions and thereby decoding a part of each instructioncode, that is, 6 high-order bits, it is possible to decide by a decoderwith a small logic scale whether the instruction is a CPU instruction, a16-bit DSP instruction, or a 32-bit DSP instruction. Therefore, it isnot necessary to always decode 32 bits at the same time.

The decoder includes a first decode circuit (240) for decoding 6high-order bits of an instruction register and generating the CPU decodesignal (243) and the DSP decode signal (244) and a code convertingcircuit (242) for outputting a signal obtained by coding 16 low-orderbits of an instruction register when discriminating a 32-bit DSPinstruction by the first decode circuit and a code representing that theoutput is invalid when discriminating an instruction other than the32-bit DSP instruction. The DSP decode signal and the output of the codeconverting circuit are used as the DSP control signal (20).

When noticing the point of the instruction format of the DSPinstruction, a microcomputer is formed into a semiconductor integratedcircuit including the central processing unit (2), the digital signalprocessing unit (3) to be synchronously operated by the centralprocessing unit, and the internal bus (IDB) to which the centralprocessing unit and the digital signal processing unit are connected incommon. The central processing unit is provided with execution controlmeans for executing an instruction of a first format having a first codearea (bit 9 to bit 0 of the 16-bit DSP instruction shown in FIG. 18) forspecifying data transfer to and from the digital signal processing unitfor the central processing unit and an instruction of a second formathaving a second code area (field A of the 32-bit DSP instruction shownin FIGS. 20 and 21) with the same format as the first code area and athird code area (field B of the 32-bit DSP instruction shown in FIGS. 20and 21) for specifying operational processing using the transferred dataspecified in-the second code area for the digital signal processingunit.

Thereby, when executing the instruction of the first format and theinstruction of the second format respectively, the execution controlmeans can adopt decode means having decode logic common to the first andsecond code areas, and this contributes to decrease of the logic scaleof a microcomputer.

The instruction of the first format and the instruction of the secondformat have a fourth code area (e.g. bit 15 to bit 10 in a 16-bit DSPinstruction or bit 32 to bit 26 in a 32-bit DSP instruction) forindicating tire first format or the second format.

The execution control means includes the instruction register (25) usedfor the instruction of the first format and the instruction of thesecond format in common, the decode means (240) for deciding the firstand fourth code areas or the second and fourth code areas included in aninstruction fetched by the instruction register, and execution means forperforming address computation in accordance with the decoded result andperforming the data transfer control.

The instruction register is provided with a high-order area (UIR) sharedto hold the first and fourth code areas or the second and fourth codeareas and a low-order area used to hold the third code area. The decodemeans includes means (242, 242A, and 242B) for outputting a controlsignal (248) showing that the instruction register holds the instructionof the second format in accordance with the decoded result of the fourthcode area and supplying code data in the third code area from thelow-order area to the digital signal processing unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an entire block diagram of the microcomputer of an embodimentof the present invention;

FIG. 2 is an address map of a microcomputer;

FIG. 3 is a block diagram of a CPU core showing a modulo address outputportion in detail;

FIG. 4 is a block diagram of a DSP engine;

FIG. 5 is an illustration of an instruction format and an instructioncode of a microcomputer;

FIG. 6 is a block diagram showing the connective structure between aCPU-core decoder and a DSP engine decoder;

FIG. 7 is a time chart for executing an ALU arithmetic instruction in aCPU core;

FIG. 8 is a time chart-for executing an instruction for reading datafrom a memory into a CPU core;

FIG. 9 is a time chart for executing an instruction for writing datafrom a CPU core into a memory;

FIG. 10 is a time chart for executing a DSP instruction;

FIG. 11 is a time chart for executing an instruction for reading datafrom X and Y memories into a DSP engine;

FIG. 12 is a time chart for executing an instruction for writing datafrom a DSP engine into X and Y memories;

FIG. 13 is a time chart for executing an instruction for reading datafrom a memory into a DSP engine;

FIG. 14 is a time chart for executing an instruction for writing datafrom a DSP engine into a memory;

FIG. 15 is a time chart for executing a DSP arithmetic instruction;

FIG. 16 is a time chart for continuously executing a DSP arithmeticinstruction;

FIG. 17 is a block diagram showing another embodiment corresponding toFIG. 6;

FIG. 18 is an instruction format diagram showing the code of a 16-bitDSP instruction for specifying data transfer between a built-in memoryof a microcomputer and a built-in register of a DSP engine;

FIG. 19 is an instruction format diagram showing the code of a 16-bitDSP instruction for specifying data transfer between an external memoryof a microcomputer and a built-in register of a DSP engine;

FIG. 20 is an instruction format diagram showing codes in a field andmnemonics corresponding to the codes when noticing field B of a 32-bitDSP instruction; and

FIG. 21 is an instruction format diagram showing codes in a field andmnemonics corresponding to the codes when noticing field B of a 32-bitDSP instruction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an entire block diagram of a single-chip microcomputer(single-chip microprocessor) serving as the data processor of anembodiment of the present invention.

The microcomputer shown in FIG. 1 is formed on a semiconductor substratemade of, for example, single-crystal silicon by a semiconductorintegrated circuit process. The microcomputer 1 comprises a CPU core 2serving as a central processing unit, a DSP engine 3 serving as adigital signal processing unit, an X-ROM 4, a Y-ROM 5, an X-RAM 6, aY-RAM 7, an interrupt controller 8, a bus state controller 9, built-inor on-chip peripheral circuits 10 and 11, an external memory interface12, and a clock pulse generator (CPG) 13.

The X-ROM 4 and the Y-ROM 5 are read-only memories or electricallyerasable programmable memories for storing instructions or constantdata. The X-RAM 6 and the Y-RAM 7 are random access memories used totemporarily store data or used as work areas of the CPU core 2 and theDSP engine 3. The X-ROM 4 and the X-RAM 6 are generally called internalinstruction/data X memories and the Y-ROM 5 and the Y-RAM 7 aregenerally called internal instruction/data Y memories. The Y-ROM 5 andY-RAM 7 serve as first memories and the X-ROM 4 and X-RAM 6 serve assecond memories.

The bus of the microcomputer 1 of this embodiment includes the internaladdress bus IAB and internal data bus IDB which are connected to theexternal memory interface 12, the internal address bus XAB and internaldata bus XDB which are not connected to the external memory interface12, the internal address bus YAB and internal data bus YDB which are notconnected to the external memory interface 12, and a peripheral addressbus PAB and a peripheral data bus PDB which are used for the built-inperipheral circuits 10 and 11. A control bus, though not illustrated, isprovided correspondingly to three sets of address bus and data busrespectively.

The data bus IDB connectable with the outside of a chip through theexternal memory interface 12 is connected to the CPU core 2, and aninterrupt signal 80 is supplied to the CPU core 2 from the interruptcontroller 8. The CPU core 2 supplies a control signal 20 forcontrolling the DSP engine 3 to the DSP engine 3. Moreover, the CPU core2 outputs an address signal to the address bus IAB connectable with theoutside of a chip through the external memory interface 12 and theaddress buses XAB and YAB which are not connected to the external memoryinterface 12. The CPU core 2 is operated by using non-overlap two-phaseclock signals Clock 1 and Clock 2 output from a clock pulse generator(CPG) 13 as operation reference clock signals. Though the detail of theCPU core 2 is described later, a register file 21, an arithmetic andlogic unit (ALU) 22, an address adder (Add-ALU) 23, a decoder 24, and aninstruction register (IR) 25 are typically illustrated in the CPU core 2of FIG. 1.

The register file 21 is optionally used as an address register or dataregister and includes a program counter and a control register. Thedecoder 24 decodes an instruction fetched by the instruction register 25and generates an internal control signal (not illustrated in FIG. 1) andthe control signal 20. The instruction register (IR) 25 comprises a16-bit high-order area (UIR) and a 16-bit low-order area (LIR). Thoughthe detail is described later, the value of the low-order area (LIR) isselectively made shiftable to the high-order area (UIR). A sequencecontrol circuit is not illustrated which controls an instructionexecution procedure when an exception such as an interrupt occurs orcontrols save or return of an internal state for occurrence of theexception by using hardware.

The DSP engine 3 is connected to the data buses IDB, XDB, and YDB andoperated by using the clock signals Clock 1 and Clock 2 as operationreference clock signals. Though the detail of the DSP engine 3 isdescribed later, a data register file 31, an arithmetic and logic unitand shifter (ALU/Shifter) 32, a multiplier (MAC) 33, and a decoder 34are typically illustrated in the DSP engine 3 of FIG. 1. The dataregister file 31 is used for multiply and accumulate operation. Thedecoder 34 decodes the control signal 20 supplied from the CPU core 2and generates an internal control signal (not illustrated in FIG. 1) ofthe DSP engine 3.

The X-ROM 4 and the X-RAM 6 are connected to the address bus IAB and thedata buses IDB and XDB. The Y-ROM 5 and the Y-RAM 7 are connected to theaddress buses IAB and YAB and the data buses IDB and YDB. The built-inmemories (X-ROM 4 and X-RAM 6, and Y-ROM 5 and Y-RAM 7) are divided intothe X-memories 4 and 6 and the Y-memories 5 and 7 by considering themultiply and accumulate operation by the DSP engine 3 and madeaccessible in parallel by the internal buses XAB and XDB, and YAB andYDB respectively. Moreover, because the internal buses XAB and XDB, andYAB and YDB are separated from the buses IAB and IDB to be interfacedwith the outside of the chip of the microcomputer 1, access to anexternal memory is possible in parallel with the access to the Xmemories 4 and 6 and the Y memories 5 and 7. The X memories 4 and 6 andthe Y memories 5 and 7 are used as a temporary data storage area of aconstant data storage area for the multiply and accumulate operation bythe DSP engine. It is needless to say that the X-RAM and Y-RAM can beused as temporary data storage areas or work areas of the CPU core 2.

The interrupt controller 8 receives an interrupt a request signal(Interrupts) 81 from the built-in peripheral circuit 10 or 11,arbitrates and accepts an interrupt request in accordance with theinformation for priority setting of various interrupt requests andmasking for interrupt requests, outputs an interrupt vector addresssignal 82 corresponding to an accepted interrupt request to the addressbus IAB, and moreover outputs the interrupt signal 80 to the CPU core 2.

The bus state controller 9 is connected to the address buses IAB and PABand the data buses IDB and PDB and controls the interface between thebuilt-in peripheral circuits 10 and 11 connected to the address bus PABand the data bus PDB on one hand and the CPU core 2 on the other.

The external memory interface 12 is connected to the address bus IAB andthe data bus IDB and moreover connected to an external address bus (notshown) at the outside of the chip of the microcomputer 1 to control theinterface with an external unit.

FIG. 2 shows a map of the address space of the microcomputer 1.

The microcomputer of this embodiment controls an address space specifiedwith 32 bits. The address bus IAB has a width of 32 bits. The addressspace includes an exception vector table area, an X-ROM address space(address space assigned to the X-ROM 4), an X-RAM address space (addressspace assigned to the X-RAM 7), a Y-ROM address space (address spaceassigned to the Y-ROM 5), a Y-RAM address space (address space assignedto the Y-RAM 7), and a on-chip peripheral register field (address spaceto which the built-in peripheral circuits 10 and 11 are assigned). Inthe case of FIG. 2, 24 KB are assigned to the X-ROM 4, 4 KB are assignedto the X-RAM 6, 24 KB are assigned to the Y-ROM 5, and 4 KB are assignedto the Y-RAM 7.

According to FIG. 2, the address space of the microcomputer 1 can beassigned as follows.

An exception vector table area is assigned to a 256B area in addressspaces of H′100000000 to H′000003FF shown by the hexadecimal notation. Anormal address space usable by a user is assigned to H′00000400 toH′01FFFFFF. The normal address space is used as a memory areaconnectable with the outside of the microcomputer 1. An X-ROM addressspace is assigned to H′02000000 to H′02005FFF. An X-RAM address space isassigned to H′02006000 to H′02006FFF.

H′02007000 to H′02007FFF are used as an X-RAM_Mirror address space.Accessing the X-RAM_Mirror address space actually represents the accessto an X-RAM address space of H′02006000 to H′02006FFF. H′02008000 toH′0200FFF are used as X-RAM and RAM_Mirror address spaces. Accessingthese address spaces actually represent the access to X-ROM and X-RAMaddress spaces of H′02000000 to H′02007FFF. A Y-ROM address space isassigned to H′02010000 to H′02015FFF. A Y-RAM address space is assignedto H′02016000 to H′02016FFF.

H′02017000 to H′02017FFF are used as a Y-RAM_Mirror address space.Accessing the Y-RAM_Mirror address space actually represent the accessto a Y-RAM address space of H′0201600 to H′02016FFF. H′02018000 toH′0201FFFF are used as a Y-ROM and RAM_Mirror address spaces. Accessingthese spaces actually represents the access to Y-ROM and Y-RAM addressspaces of H′02010000 to H′02017FFF. A normal address space is assignedto H′02020000 to H′07FFFFFFF.

A reserved area is assigned to H′08000000 to H′1FFFFFFFF. The reservedarea cannot be accessed in the case of a user chip (actual chip) but itis assigned as an ASE address space (control address space foremulation) in the case of an evaluation chip (for evaluation used foremulation or the like). A normal address space is assigned to H′20000000to H′27FFFFFFF. A reserved area is assigned to H′28000000 to H′FFFFFDFF.A on-chip peripheral register area to which a register address value ofa built-in peripheral circuit should be assigned is assigned toH′FFFFFE00 to H′FFFFFFFF.

FIG. 3 shows a block diagram of the CPU core 2 whose modulo addressoutput portion is shown in detail.

A portion enclosed by a broken line in FIG. 3 represents a moduloaddress output portion 200. The modulo address output portion 200 is acircuit block for performing address update and output operations foroutputting a value output from a modulo address register (e.g. AOX) toan address bus (e.g XAB) through a buffer (e.g. MABX) and moreoveradding a value output from the modulo address register (AOX) by summingmeans (e.g. ALU) and storing the value in the modulo address register(AOX) again and sequentially updates and generates a data access addressfor repetitive operation such as multiply and accumulate operation. Thecircuit block shown as a random logic circuit 201 is a circuit blockincluding the decoder 24 in FIG. 1, the sequence control circuit, and acontrol register and a status register.

In FIG. 3, C1, C2, DR, A1, B1, A2, B2, and DW are typical buses in theCPU core 2. The CPU core 2 and the data bus IDB are interfaced throughthe instruction register (IR) 25 and a data buffer 203. An instructionfetched by the instruction register (IR) 25 is supplied to the decoder24 or the like included in the random logic circuit 201. The CPU core 2and the address bus IAB are interfaced through a program counter (PC)204 and an address buffer 205. The CPU core 2 and the address bus XABare interfaced through memory address buffer (MABX) 206, and the CPUcore 2 and the address bus YAB are interfaced through a memory addressbuffer (MABY) 207.

The input path of address information to the address buffer 205 can beselected out of the buses C1, A1, and A2, and the input path of addressinformation to the memory address buffers 206 and 207 ban be selectedout of the buses C1, C2, A1, and A2. An arithmetic unit (AU) 208 is usedfor increment of the program counter 204. In FIG. 3, symbol 209represents a general-purpose register (Reg.), 210 represents an indexregister (Ix) used for indexing an address, 211 represents a indexregister (Iy) also used for indexing an address, 212 represents an adder(PAU) dedicated to address computation, and 213 represents an arithmeticand logic unit (ALU).

A control bit MXY designates address bus XAB or YAB to which moduloarithmetic should be applied. The address bus XAB is designated by thelogical value “1” of the control bit MXY. The address bus YAB isdesignated by the logical value “0” of the control bit MXY.

A control bit DM designates whether to perform modulo arithmetic. It isdesignated to perform the modulo arithmetic by the logical value “1” ofthe control bit DM. Moreover, it is designated by the logical value “0”of the control bit DM that modulo arithmetic is not performed. A modulostart address register (MS) 214 stores a modulo arithmetic start addressand a modulo end address register (ME) 215 stores a modulo arithmeticend address.

A modulo address register (A0x, A1x) 216 is a current address registerfor storing a current modulo address. Numeral 217 represents acomparator (CMP) for comparing a value of the modulo end addressregister (ME) 215 with a value of the modulo start address register(A0x, A1x) 216. Numeral 218 represents an AND gate for the logicalproduct of the output from the comparator 217, and control bits MXY andDM. Symbol 219 represents a selector for selecting a value of the bus Cland a value of the modulo start address register (MS) 214. These valueare used for the modulo arithmetic for the address bus XAB.

The selector 219 selects a value of the register (MS) 214 according tothe logical-value “1” output of the AND gate 218 and supplies theselected value to the modulo address register (A0x, A1x) 216. Either A0xor A1x of the modulo address register 216 is selected and used.

A modulo address register (A0y, A1y) 226 is a current address registerfor storing a current modulo address. Symbol 227 represents a comparator(CMP) for comparing a value of the modulo address register (ME) 215 witha value of the modulo address register (A0y, A1y) 216. Symbol 228represents an AND gate for the logical product of the output of thecomparator 227, and the inversion of the control bit MXY and the controlbit DM. Symbol 229 represents a selector for selecting a value of thebus C and a value of the modulo start address register (MS) 214. Thesevalues are used for the modulo arithmetic for the address bus YAB.

The selector 229 selects a value of the register (MS) 214 in accordancewith the logical-value “1” output of the AND gate 228 and supplies theselected value to the modulo address register (A0y, A1y) 226. Either A0yor A1y of the modulo address register 226 is selected and used.

The OP Code entered in the random logic circuit 201 represents aninstruction code supplied from the instruction register 25 and the CONSTrepresents a constant value.

An operation is described below as the modulo arithmetic by the CPU core2, in which address information to be supplied to the address bus XAB isgenerated by modulo arithmetic by using, for example, the modulo addressregister (A0x) 216.

First, the modulo arithmetic start address is written in the modulostart address register (MS) 214 and the modulo arithmetic end address iswritten in the modulo end address register (ME) 215. An address valuefor starting modulo arithmetic is written in the modulo address register(A0x). Then, to apply modulo arithmetic to an address of the address busXAB, the logical value “1” is written in the control bit MXY fordeciding which the modulo-arithmetic should be applied to, an address ofthe XAB or an address of the YAB (when applying the modulo arithmetic tothe address bus YAB, the logical value “0” is written in the control bitMXY). Finally, the logical value “1” is written in the control bit DMfor deciding whether to perform modulo arithmetic.

A modulo arithmetic instruction is described as, for example, MOVS.W@Axor Dx. In the case of this instruction description, Ax is used for themodulo address register (A0x) 216 or modulo address register (A1x) 216and Dx corresponds to a register in the DSP engine 3. In FIG. 3, Dx isnot illustrated.

When the modulo arithmetic instruction is executed, a value is read bythe modulo address register (A0x) 216 and input to the memory addressbuffer (MABX) 206 and the arithmetic and logic unit (ALU) 213. The valueinput to the memory address buffer (MABX) 206 is directly output to theaddress bus XAB to designate an address of the XROM 4 or XRAM 6.

A value of the index register (Ix) 210 or a constant is added to thevalue of the modulo address register (A0x) 216 input to the arithmeticand logic unit (ALU) 213. Addition with the index register (Ix) 210 isperformed when an instruction MOVS.W@(Ax, Ix) or Dx is executed. Aconstant (Const) is added when an instruction MOVS.W @Ax, Dx or the likeis executed. The addition result is output from the arithmetic and logicunit (ALU) 213. The value output from the arithmetic and logic unit(ALU) 213 is input to the selector 219. Another input of the selector219 is the modulo arithmetic start address stored in the modulo startaddress register (MS) 214.

Whether the output of the selector 219 serves as an output of thearithmetic and logic unit (ALU) 213 or that of the modulo start addressregister (MS) 214 is determined as shown below.

A value of the modulo address register (A0x) 216 and a value of themodulo address register (ME) 215 are always compared by the comparator(CMP) 217. When these values are matched each other, the logical value“1” is output from the comparator (CMP) 217. When they are mismatched,the logical value “0” is output from the comparator. The logical productof a value output from the comparator (CMP) 217 is computed by the ANDgate 218 together with the control bits DM and MXY (in this case,because both DM and MXY have the logical value “1”, a value of thecomparator 217 is directly output from the AND gate 218) and input tothe selector 219. The selector 219 selects a value of the modulo startaddress register (MS) 214 when a value input from the AND gate 218 isthe logical value “1” but selects a value output from the arithmetic andlogic unit (ALU) 213 when the value input from the AND gate 218 is thelogical value “0”.

While a value input from the AND gate 218 is the logical value “0”, theselector 219 continuously selects a value output from the arithmetic andlogic unit (ALU) 213. Therefore, a value output to the address bus XABis sequentially updated. When a value of the modulo end address register(ME) 215 matches a value of the modulo address register (A0x) 216, avalue input to the selector 219 from the AND gate 218 is set to thelogical value “1” to select a value of the modulo start address register(MS) 214. Thereby, the modulo address register (A0x) 216 is initializedby the value of the modulo start address register (MS) 214.

In the above description of the modulo arithmetic, the operation whenusing the modulo address register (A0x) 216 is described. However, it isalso possible to designate Ax in the modulo arithmetic instructionMOVS.W@Ax or Dx to the modulo address register (A1x) 216. Moreover, bydesignating the logical value “0” to the control bit MXY, moduloarithmetic can be performed for the address bus YAB. In this case, Ax inthe modulo arithmetic instruction MOVS.W@Ax or Dx must be changed to avalue Ay for designating the modulo address register (A0y) 226 or (A1y)226. When designating 0 to the control bit DM, it is possible to inhibitthe execution of modulo arithmetic.

FIG. 4 shows a block diagram of the DSP engine 3.

The circuit block shown as a random logic circuit 301 includes thedecoder 34 and control circuit in FIG. 1 and moreover, a controlregister and a status register. Moreover, the DSP engine 3 is providedwith an arithmetic and logic unit (ALU) 302, a shifter (SFT) 303, amultiplier (MAC) 304, a register (Reg.) 305, a register (A0, A1) 306, aregister (Y0, Y1) 307, a register (X0, X1) 308, a memory data buffer(MDBI) 309, a memory data buffer (MDBX) 310, and a memory data buffer(MDBY) 311.

The memory data buffer (MDBY) 311 connects the data bus YDB with the busD2. The memory data buffer (MDBX) 310 connects the data bus XDB with thebus D1. The memory data buffer (MDBX) 309 connects with the data bus IDBand the buses C1, D1, A1, and B1.

The multiplier (MAC) 304,inputs data from the buses A1 and B1 andoutputs the multiplication result of the data to the buses C1 and D1.The shifter (SFT) 303 inputs data from the bus A2 and outputs the shiftoperation result to the bus C2. The arithmetic and logic unit (ALU) 302inputs data from the buses A2 and B2 and outputs the operation result tothe bus C2.

FIG. 5 shows an instruction format and an instruction code included inthe instruction set of the microcomputer 1.

The microcomputer 1 supports the following two types of instructions:CPU instruction (first instruction) and DSP instruction (secondinstruction). All CPU instructions and some of DSP instructions areinstruction codes of 16-bit length (first bit length). Remaining DSPinstructions are instruction codes of 32-bit length (second bit length).

In this specification, a CPU instruction is defined as an instruction tobe exclusively executed by the CPU core 2 without operating the DSPengine 3. A DSP instruction is defined as an instruction to be executedby the DSP engine 3 by making the CPU core 2 perform some processingsuch as address arithmetic or operand access.

In the case of a CPU instruction, 4 high-order bits of an instructioncode are assigned to an address space from “0000” to “1110”. In the caseof a DSP instruction, 4 high-order bits of an instruction code are allassigned to “1111”. Moreover, in the case of even a DSP instruction inwhich 6 high-order bits of an instruction code are assigned to “111100”and “111101”, it has a 16-bit instruction code. An instruction in which6 high-order bits of an instruction code are assigned to “111110” has a32-bit instruction code. Because no instruction is assigned to anaddress space in which 6 high-order bits of an instruction code are“111111” and therefore, the address space is a vacant area (undefinedinstruction area). It is possible to further extend an instruction codeby using the area in future.

As understood from the instruction format, by decoding 6 high-order bitsof each instruction, it is possible to judge by a decoder with a smalllogic scale whether the instruction concerned is a CPU instruction, a16-bit DSP instruction, a 32-bit DSP instruction, or an undefinedinstruction.

In the CPU instruction format in FIG. 5, nnnn represents adestination-operand designated area, ssss represents a source-operanddesignated area, dddd represents a displacement designated area, andiiiiiiii represents an immediate-value designated area. In the case ofan ADD instruction, nnnn is also used as a source-operand designatedarea and arithmetic results are stored in nnnn. The modulo arithmeticinstruction described by referring to FIG. 3 corresponds to theinstruction MOVS.W@R2 or A0 in FIG. 5. However, in the case of theinstruction description in FIG. 5, the form of describing operanddesignation is different from the content described in FIG. 3. However,this is mere difference in type but the essense is the same.

FIG. 6 shows a connective structure between the decoder 24 of the CPUcore 2 and the decoder 34 of the DSP engine 3.

Instruction fetch by the microcomputer 1 is performed by the instructionregister (IR) 25 every 32 bits. The decoder 24 is provided with a firstdecode circuit 240, a second decode circuit 241, and a code conversioncircuit 242.

The first decode circuit 240 decodes a value in the high-order 16-bitarea (UIR) of the instruction register (IR) 25 and generates a CPUdecode signal 243, a DSP decode signal 244, a code conversion controlsignal 245, and shift control signal 246 in accordance with the factthat the instruction concerned is a CPU instruction, a 16-bit DSPinstruction, or a 32-bit DSP instruction.

The second decode circuit 241 decodes the CPU decode signal 243 andgenerates various internal control signals (CPU control signals) 247 forselecting an arithmetic unit or a register in the CPU core 2.

When the code conversion circuit 242 is activated by the code conversioncontrol signal 245, it compresses or directly outputs the number of bitsfor the information held by the low-order 16-bit area (LIR) of theinstruction register (IR) 25. When the circuit 242 is deactivated by thecode conversion control signal 245, it outputs information(non-operation code) representing that its output is invalid.

It is also possible to realize the code conversion circuit 242 by aselector in order to output a non-operation code instead of a value ofthe low-order 16-bit area (LIR) when the signal 245 is inactive. The DSPdecode signal 244 and an output of the code conversion circuit 242 aresupplied to the decoder 34 of the DSP engine 3 as the DSP control signal20. The first decode circuit 240 is able to decide that the instructionconcerned is a CPU instruction, a 16-bit DSP instruction, or a 32-bitDSP instruction by decoding 6 high-order bits stored in the high-order16-bit area (UIR) of the instruction register (IR) 25.

When a decoded instruction is a 16-bit instruction, the code conversioncontrol signal 245 is deactivated and thereby, the code conversioncircuit 242 outputs a non-operation code representing that output isinvalid. When the decoded instruction is a 16-bit instruction, the shiftcontrol signal 246 is activated and the instruction register (IR) 25receiving the signal 246 shifts a value in the loworder 16-bit area(LIR) to the high-order 16-bit area (LIR) to use the shifted instructionas the whole or part of the instruction to be next executed.

For example, a case is described below in which a 16-bit CPU instructionis stored in the high-order 16-bit area of the instruction register IRand a highorder 16-bit instruction code of a 32-bit DSP instruction isstored in the low-order bit area LIR. First, the 16-bit CPU instructionstored in the high-order 16-bit area UIR is decoded by the first decodecircuit 240, the CPU core 2 executes the instruction according to theresult, and the high-order 16-bit instruction code data of the 32-bitDSP instruction stored in the low-order 16-bit area LIR is transferredto the high-order 16-bit area UIR. In this case, the random logiccircuit 201 makes the arithmetic operation unit (AU) 208 execute addressarithmetic of an address to be stored in the program counter PC. Theprogram counter PC stores an address following the address arithmeticresult computed by the arithmetic unit AU 208. In accordance with theaddress stored in the program counter PC, the low-order 16-bitinstruction code data of the 32-bit DSP instruction is transferred fromthe instruction memory storing the data to the low-order 16-bit area LIRof the instruction register IR. Thereby, the 32-bit DSP instruction isstored in the instruction register IR. Then, the 32-bit DSP instructionstored in the instruction register IR is supplied to the decoder 34 ofthe DSP engine 3 through the decoder 24.

Moreover, as other method, a plurality of instruction prefetch puffersare provided in the CPU core 2 through they are not illustrated. Theseinstruction prefetch buffers prefetch the instructions to be executedseveral cycles ahead from an instruction currently executed. When theseprefetch buffers are used and the high-order 16-bit instruction codedata of the 32-bit DSP instruction is transferred from the low-orderarea LIR to the high-order 16-bit area UIR as described above, therandom logic circuit 201 selects an instruction prefetch buffer by whichthe low-order 16-bit instruction code data of the 32-bit DSP instructionis fetched. The low-order 16-bit instruction code data of the 32-bit DSPinstruction is read out of the selected instruction prefetch buffer andstored in the low-order 16-bit area LIR of the instruction register IR.

When the decoded instruction is a 16-bit CPU instruction, the DSP decodesignal 244 is used as a code representing non-operation. When thedecoded instruction is a 16-bit DSP instruction, the second decodecircuit 241 generates the CPU control signal 247 in accordance with theCPU decode signal 243 and the decoder 34 generates a control signal inthe DSP engine 3 by substantially decoding the DSP decode signal 244.When the decoded instruction is a 32-bit DSP instruction, the seconddecode circuit 241 generates the CPU control signal 247 in accordancewith the CPU decode signal 243 and the decoder 34 generates a controlsignal in the DSP engine 3 by decoding the DSP decode signal 244 and anoutput of the code conversion circuit 242.

The instruction set of the microcomputer 1 includes instruction codes of16 bit length and 32 bit length. However, because a 16-bit instructionis different from a 32-bit instruction in processing, the operation ofeach case is separately described below in detail.

First, the case of a 16-bit instruction is described.

The first decode circuit 240 decodes 16 high-order bits of a 32-bitinstruction code fetched by the instruction register (IR) 25. The firstdecode circuit 240 can detect that the instruction concerned is a16-bits instruction unless 6 high-order bits of an instruction code are“111110” or “11111”. In this case, the shift control signal 246 forshifting the instruction code data of low-order 16-bit area LIR of theinstruction register (IR) 25 is activated together with outputs of theCPU decode signal 243 and DSP decode signal 244.

The instruction register (IR) 25 receiving the activated shift controlsignal 246 shifts an instruction code stored in the low-order 16-bitarea LIR to the high-order 16-bit area UIR. The shifted instruction codeis then decoded by the first decode circuit 240. The CPU decode signal243 output from the decoder 24 is output to the second decode circuit241 and the DSP decode signal 244 is supplied to the DSP engine 3. Whenthe first decode circuit 240 detects a 16-bit instruction, itdeactivates the code conversion control signal 245. Thereby, the codeconversion circuit 242 generates a code showing that a low-order 16-bitinstruction code is invalid as a part of the DSP control signal 20.

When the DSP engine 3 receives the DSP decode signal 244 output from thefirst decode circuit 240 and a code signal output from the codeconversion circuit 242 as the DSP control signals 20, decoder 34 decodesthe DSP control signals 20. In the case of a 16-bit DSP instruction, theDSP control signal output from the code conversion circuit 242 serves asa signal representing invalidness. Therefore, the decoder 34 notices theDSP decode signal 244 and outputs control signals for the multiplier(MAC) 304, arithmetic and logic unit (ALU) 302, and shifter (SFT) 303 inthe DSP engine 3. The DSP engine 3 performs arithmetic processing inaccordance with these control signals.

Then, the case of a 32-bit instruction is described below.

The first decode circuit 240 in the CPU core 2 stores a 32-bitinstruction code in the instruction register (IR) 25. Then, the firstdecode circuit 240 decodes 16 high-order bits of the instruction codeand outputs the decode signals 243 and 244. Because the first decodecircuit 240 can detect that the instruction concerned is a 32-bitinstruction when a high-order 16-bit code of the instruction code is setto “111110”, it activates the code conversion control signal 245.Thereby, the code conversion circuit 242 applies code conversion to alow-order 16-bit instruction code of the instruction register (IR) 25.Code-converted information is supplied to the DSP engine 3 together withthe DSP decode signal 244 as the DSP control signals 20. The decoder 34decodes the DSP control signals 20 and generates a control signal in theDSP engine 3. The decoders 24 and 34 can be realized by, for example, arandom logic circuit.

FIG. 17 shows another embodiment corresponding to the embodiment in FIG.6.

In the case of the embodiment in FIG. 6, it is described thatinstruction data in the low-order area LIR of the instruction register25 is shifted to the high-order area UIR.

In the case of the embodiment in FIG. 17, two-stage series instructionprefetch buffers 250 and 251 constituting an instruction prefetch queueare provided between the instruction register 25 and the internal databus IDB and the data held by the instruction prefetch buffers 250 and251 is selected by a selector 252 and supplied to the register 25. Eachof the instruction prefetch buffers 250 and 251 and the instructionregister 25 holds data every 32 bits and the holding operation iscontrolled by control signals φ1 to φ3 (synchronizing with CLK1).

Though not illustrated, each of the instruction prefetch buffers 250 and251 and the instruction register 25 has a master-slave structure. Themaster stage latches an input synchronously with the rise of acorresponding control signal and the slave stage latches an inputsynchronously with the trailing edge of a corresponding control signal.Thereby, instruction data before and after prefetched is stored in thetwo-stage series instruction prefetch buffers 250 and 251.

The selector 252 selects 32-bit instruction data to be supplied to aport Pa or 32-bit instruction data to be supplied to a port Pb inaccordance with a selection control signal φ4 and supplies it to theinstruction register 25. The 32-bit instruction data using a high-order16-bit area UPB1 of the instruction prefetch buffer 250 as a low-orderside and a low-order 16-bit area LPB2 of the instruction prefetch buffer251 as a high-order side is supplied to the port Pa. The 32-bitinstruction data stored in the instruction prefetch buffer 251 isdirectly supplied to the port Pb.

Thereby, when the instruction prefetch buffer 251 holds a 32-bit DSPinstruction, the selector 252 can set the 32-bit DSP instruction to theinstruction register 25 by selecting an output of the port Pb.

When the instruction prefetch buffer 251 holds a 16-bit DSP instructionor a 16-bit CPU instruction in the high-order area UPB2, the selector252 can set the 16-bit instruction to the high-order area UIR of theinstruction register 25 by selecting an output of the port Pb.

When the instruction prefetch buffer 251 holds a 16-bit DSP instructionor a 16-bit CPU instruction in the low-order area LPB2, the selector 252can set the 16-bit instruction to the high-order area UIR of theinstruction register 25 by selecting an output of the port Pa.

When the instruction prefetch buffer 251 holds a high-order 16-bitinstruction code of a 32-bit DSP instruction in the low-order area LPB2and the instruction prefetch buffer 250 holds a low-order 16-bitinstruction code of the 32-bit DSP instruction in the high-order areaUPB1, the selector 252 can set the 32-bit DSP instruction to theinstruction register 25 by selecting an output of the port Pa.

In FIG. 17, symbol 253 represents a control logic for generating latchcontrol signals φ1 and φ2 of the instruction prefetch buffers, a latchcontrol signal φ3 of the instruction register 25, and the selectioncontrol signal φ4. The control logic 253 generates the control signal248 showing a 16-bit instruction or a 32-bit instruction and the controlsignals φ1 to φ4 in accordance with the state of an instruction coderemaining unexecuted in each area of the instruction prefetch buffers250 and 251. The control logic 253 constitutes a part of control logicfor instruction fetch. The control signal 248 is generated when thefirst decode circuit 240 decodes 6 high-order bits of instruction codedata supplied from the high-order area UIR of the instruction register25 and its detail is described later.

Instruction code data is set to the instruction register 25 by thecontrol logic 253 as shown below.

Instruction fetch from the outside is performed at the instruction fetchtiming of the CPU core 2 (for example, at an instruction fetch stage IFof a plurality of pipeline stages to be mentioned later) when theinstruction prefetch buffer 250 has a space for newly storing 32-bitinstruction code data. When instruction fetch is performed at thetiming, unexecuted instructions are left in the instruction prefetchbuffer 251.

When both instruction codes stored in the areas UPB2 and LPB2 of theinstruction prefetch buffer 251 are under the first state in which thecodes are not executed yet, a 32-bit output of the instruction prefetchbuffer 251 is selected by the selector 252 through the port Pb and setto the instruction register 25.

When the instruction code stored in the low-order area LPB2 of theinstruction prefetch buffer 251 is under the second state in which thecode is not executed yet, instruction code data in the high-order areaUPB1 prefetched by the instruction prefetch buffer 250 and instructioncode data in the low-order area LPB2 of the instruction prefetch buffer251 are set to the instruction register 25 through the port Pa.

Under the above first state, when the decode circuit 240 decodes theinstruction code data set to the high-order area UIR of the instructionregister 25 and resultingly, the data is a 32-bit instruction, 32-bitinstruction code data is directly transferred to the instructionprefetch buffer 251. However, when a 16-bit instruction is detected asthe result of decoding the instruction decode data, no data is shiftedfrom the instruction prefetch buffer 250 to the next-stage buffer 251.

Under the above second stage, the 32-bit instruction code dataprefetched by the instruction prefetch buffer 250 is directly shifted tothe instruction prefetch buffer 251 and set after data is set to theinstruction register 25 through the port Pa. After the data is shiftedand set, instruction code data is prefetched by the instruction prefetchbuffer 250 at the next instruction prefetch timing unless any unexecutedinstruction code data is left in the instruction prefetch buffer 250.

According to the above control, unprocessed instruction code data is setto the instruction register 25 after the instruction fetch timing. Inthis case, even if an instruction to be executed is any one of a 16-bitCPU instruction, 16-bit DSP instruction, and 32-bit DSP instruction, 16high-order bits of the instruction is supplied to the first decodecircuit 240 without fail.

The code conversion circuit 242 described in FIG. 6 comprises a selector242A and a code conversion logic 242B in FIG. 17. Moreover, the firstdecode circuit 240, in the description of FIG. 6, generates the controlsignals 245 and 246 whose levels are controlled depending on whether theinstruction code decoded by the circuit 240 is a 16-bit instruction ornot. However, the embodiment in FIG. 17 outputs the control signal 248for discriminating whether an instruction code decoded by the circuit240 is a 16-bit instruction or a 32-bit instruction (in this embodiment,a 32-bit instruction is a DSP instruction). The selector 242A selects ano-operation code NOP and supplies it to the code conversion logic 242Bwhen the control signal 248 represents a 16-bit instruction but itsupplies an instruction code in the low-order area LIR of theinstruction register 25 to the code conversion logic 242B when thecontrol signal 248 represents a 32-bit DSP instruction. The codeconversion logic 242B, though not restricted, corrects part ofinstruction code data of the low-order area LIR of the instructionregister 25, for example, code information for selecting a register intoa form suitable for the decoder 34 of the DSP engine 3 and then outputsit.

In the case of the embodiment in FIG. 17, the first decode circuit 240decodes the 16-bit instruction code data held by the high-order area UIRof the instruction register 25 and supplies the CPU decode signal 243obtained through the decoding to the second decode circuit 243 andmoreover, supplies the DSP decode signal 244 to the decoder 34. The CPUdecode signal 243 is made significant for any one of a CPU instructionand a DSP instruction and supplied to the second decode circuit 241. Thesecond decode circuit 241 decodes the CPU decode signal 243 and outputscontrol information for address computation or data processing to beperformed by the CPU core 2 or selection control information of anaddress bus or data bus for accessing the internal memory X-ROM 4, Y-ROM5, X-RAM, Y-RAM, and an external memory. As described above, the CPUcore 2 selects address arithmetic or a data path necessary for a DSPinstruction.

The DSP decode signal 244, as described above, is a decode signal to bemade significant when an instruction code to be supplied to the firstdecode circuit 240 is code data for a DSP instruction. The significantDSP decode signal 244 includes information for designating a register orthe like in the DSP engine 3 for transfer data to and from a memory tobe accessed in accordance with the address computation performed by theCPU core 2. When the instruction code to be supplied to the first decodecircuit 240 is a CPU instruction, the DSP signal 244 is converted into acode representing invalidness.

The code of the DSP instruction included in the instruction set of themicrocomputer 1 is described below more minutely. FIGS. 18 and 19 showthe instruction code of a 16-bit DSP instruction respectively. FIGS. 20and 21 show the instruction code of a 32-bit DSP instructionrespectively. As described above, in the case of a DSP instruction, 4high-order bits of the instruction code are assigned to “1111”. In thecase of a 16-bit DSP instruction, 6 high-order bits of the instructioncode are assigned to “111100” and “111101”. In the case of a 32-bit DSPinstruction, 6 high-order bits of the instruction code are assigned to“111110”.

The instruction format of the 16-bit DSP instruction shown in the firstspace (X Side of Data Transfer) in FIG. 18 represents a data transferinstruction used between an X memory (X-ROM 4 or X-RAM 6) and a built-inregister of the DSP engine 3 and the instruction format shown in thesecond space (Y Side of Data Transfer) represents a data transferinstruction used between a Y memory (Y-ROM 5 or Y-RAM 7) and a built-inregister of the DSP engine 3. In the above formats, Ax and Ay designatea register included in the register array 209 (see FIG. 3) in the CPUcore 2, Ax=“0” designates a register R4, Ax=“1” designates a registerR5, Ay=“0” designates a register R6, and Ay=“1” designates a registerR7. Dx, Dy, and Da respectively designate a register included in the DSPengine, Dx=“0” designates a register C0, Dx=“1” designates a registerX1, Dy=“0” designates a register Y0, Dy=“1” designates a register Y1,Da=“0” designates a register A0, and Da=“1” designates a register A1. Ixand Iy represent an immediate value respectively.

The instruction format of a 16-bit DSP instruction shown in FIG. 19represents a data transfer instruction used between a memory (not shown)connected to an external unit of the microcomputer 1 and a built-inregister of the DSP engine 3. As designates a register included in theregister array 209 (see FIG. 3) built-in the CPU core 2. As designates aregister included in the register X1, X0, Y1, Y0, A1, or A0, or aregister array 305 (see FIG. 4).

The format of a 32-bit DSP instruction is roughly divided into an area(bit 31 to bit 26) of the code “111110” showing a 32-bit DSPinstruction, field A (bit 25 to bit 16), and field B (bit 15 to bit 0).FIG. 20 shows codes in field A and mnemonics corresponding to field Awhen noticing field A and FIG. 21 shows codes in field B and mnemonicscorresponding to field B when noticing field B.

The codes in field A shown in FIG. 20 are the same as those of bit 9 tobit 0 of the 16-bit DSP instruction shown in FIG. 18. The codes in fieldA shown in the first space (X Side of Data Transfer) in FIG. 20 specifythe data transfer between an X memory (X-ROM 4 or X-RAM 6) and abuilt-in register of the DSP engine 3 and the codes in field A shown inthe second space (Y Side of Data Transfer) specify the data transferbetween a Y memory (Y-ROM 5 or Y-RAM 7) and a built-in register of theDSP engine 3. The contents designated by the bits Ax, Ay, Dx, Dy, and Daincluded in field A are the same as those in FIG. 18.

The codes in field B shown in FIG. 21 specify arithmetic operation,logical operation, shift operation, and processing such as load/storebetween registers. For example, the codes specify the operations such asmultiplication (PMULS), subtraction (PSUB), addition (PADD), round(PRND), shift (PSHL), logical multiply (PAND), exclusive OR (XOR),logical add, increment (PINC), decrement (PDEC), and clear (CLR)performed in the DSP engine 3 or load (PLDS) and store (PSTS) performedin the DSP engine 3. The third space (3 Operand Operation withCondition) in FIG. 21 shows conditional codes and it is possible toselect a logical value or disregard of a DC (data complete) bit (bitshowing completion of data processing) as their conditions (if cc).

An actual 32-bit DSP instruction is described by optional combination ofthe codes in field B with those in field A. That is, the 32-bit DSPinstruction fetches an operand to be operated from an internal orexternal unit of the microcomputer 1 and specifies the processing foroperating the operand in the DSP engine 3. As described above, addresscomputation or selection of a data path for operand fetch is performedby the CPU 2. The code in field A for specifying operand fetch in the32-bit DSP instruction is the same as that of a 16-bit DSP instruction.The 16-bit DSP instruction is used for initialization of a register inthe DSP engine 3.

As understood by referring to the structure shown in FIG. 17 or thelike, code data in field A of a 32-bit DSP instruction is set to-thehigh-order area UIR of the instruction register 25. Moreover, a 16-bitDSP instruction having the same format as that of field A is set to thehigh-order area UIR. Therefore, in any case, it is enough for the CPUcore 2 to perform necessary address computation and selection of a datapath necessary for data fetch (or operand fetch) similarly. In otherwords, the decode circuits 240 and 241 required for data fetch (oroperand fetch) to execute a 32-bit DSP instruction and data fetch (oroperand fetch) to execute a 16-bit DSP instruction are used in common.Therefore, this also contributes to reduction of the logical scale ofthe microcomputer 1. Information for designating an internal register ofthe DSP engine 3 designated by field A of a 32-bit DSP instruction orinformation for designating an internal register of the DSP engine 3designated by a 16-bit DSP instruction is supplied to the DSP engine 3as the DSP decode signal 244. Whether to make the DSP decode signal 244significant or not is decided when the first decode circuit 240 decodes4 high-order bits of the high-order area UIR.

Then, details of the operation control in the microcomputer 1 of thisembodiment are described below by referring the instruction executiontiming charts in FIGS. 7 to 16.

The microcomputer 1 of this embodiment performs five-stage pipelineoperations of IF, ID, EX, MA, and WB/DSP stages. IF represents aninstruction fetch stage, ID represents an instruction decode stage, EXrepresents an operation execution stage, MA represents a memory accessstage, and WB/DSP represents a stage for capturing data obtained from amemory into a register of the CPU core 2 or for the DSP engine 3 toexecute a DSP instruction.

In each drawing, Instruction/Data Access represents memory accessthrough the internal buses IAB and IDB and access objects include anexternal memory of the microcomputer 1 in addition to the built-inmemories 4 to 7. X,Y Mem. Access represents memory access through theinternal buses XAB and XDB or YAB and YDB but access objects are limitedto the built-in memories 4 to 7. Isnt.Fetch represents the instructionfetch timing to the instruction register (IR) 25, Fetch. Reg. representsthe instruction register (IR) 25, Source Data Out represents a sourcedata output, Destination In represents the input timing of destinationdata, and Destination Register represents a destination register.Pointer Reg. represents a pointer register, Address Calc. representsaddress arithmetic; Data Fetch represents data fetch, and DSP Controlsignal Decode Timing represents the timing for decoding the DSP controlsignal 20 by the decoder 34.

FIG. 7 shows a time chart for executing an ALU arithmetic instruction inthe CPU core 2. In this case, ADD Rm and Rn are used as ALU arithmeticinstructions.

An address in which instructions to be executed (ADD Rm and Rn) isstored is output to the address bus IAB synchronously with the risetiming of the clock signal Clock 2 immediately before the IF stage. Inthe case of Instruction/Data Mem. Access, memory access is performed atthe IF stage. Specifically, an address designated by the address bus IABis decoded in the period between the rise of the clock signal Clock 1and the rise of the next clock signal Clock 2 and instruction access isperformed in the period between the rise of the clock signal Clock 2 andthe rise of the next clock signal Clock 1 at the IF stage. Therefore, aninstruction is output to the data bus IDB from the time when the clocksignal Clock 2 rises at the IF stage.

The instruction output to the data bus IDB is captured by theinstruction register (IR) 25 synchronously with the rise timing of theclock signal Clock 1 at the ID stage. At the ID stage, data captured bythe instruction register (IR) 25 is decoded.

A register in which source data is stored is accessed synchronously withthe rise timing of the clock signal Clock 1 at the EX stage and a valuein the register is output to the internal buses A1 and B1 of the CPUcore 2. In the case of the instructions ADD Rm and Rn, registersdesignated to Rm and Rn are serve as source registers. Rm and Rn make itpossible to designate any register in the CPU core 2 (in FIG. 3, any oneof the registers A0x, A1x, Ix, A0y, A1y, and Iy in the register 209 canbe designated as Rm or Rn).

Data output to the internal buses A1 and B1 of the CPU core 2 is addedby the arithmetic and logic unit (ALU) 213 and is result is output tothe internal bus C1 of the CPU core 2. The arithmetic result output tothe internal bus C1 of the CPU core 2 is stored in a destinationregister (the designation register is a register designated to Rn in theinstructions ADD Rm and Rn). Thus, instruction execution is completed atthree pipeline stages of IF, ID, and EX by the ALU arithmeticinstruction in the CPU core 2.

FIG. 8 shows a time chart for reading data from a memory to the CPU core2.

Operations of an instruction for reading data from a memory to the CPUcore 2 are described by taking MOV.L@Rm,Rn as an example of theinstruction. Because operations up to instruction fetch (IF) andinstruction decode (ID) are the same as those in FIG. 7, detaileddescription of them is omitted.

The data in a register serving as an address pointer synchronously withthe rise timing of the clock signal Clock 1 at the EX stage is output tothe internal bus A1 of the CPU core 2. In the case of this example, theregister serving as an address pointer is a register designated with Rm.A register which can be designated to Rm is any register included in theCPU core 2 (in FIG. 3, any one of the registers A0x, A1x, Ix, A0y, A1y,and Iy can be designated as Rm). The data output to the internal bus A1of the CPU core 2 is stored in the address buffer 205 and output to theaddress bus IAB synchronously with the rise timing of the clock signalClock 2 at the EX stage.

The data output to the internal bus A1 of the CPU core 2 is computed bythe arithmetic and logic unit (ALU) 213. In this case, the-arithmeticand logic unit (ALU) 213 performs zero addition arithmetic. Thearithmetic result is output to the internal bus C1 of the CPU core 2.The arithmetic result output to the internal bus C1 of the CPU core 2 isstored in a pointer register (in this case, a register designated withRm) synchronously with the rise timing of the clock signal Clock 2 atthe EX stage.

In the case of Instruction/Data Mem. Access, an address output to theaddress bus IAB is decoded synchronously with the rise timing of theclock signal Clock 2 at the EX stage in the period between the rise ofthe clock signal Clock 1 and the rise of the clock signal Clock 2 at theMA stage and data access is performed in the period between the rise ofthe clock signal Clock 2 and the rise of the next clock signal Clock 1at the MA stage. Therefore, data is output to the data bus IDB from thetime when the clock signal Clock 2 rises at the MA stage.

The data output to the data bus IDB is captured by the CPU core 2synchronously with the rise timing of the clock signal Clock 1 at theWP/DSP stage and output to the internal bus DW of the CPU core 2. Thedata on the internal bus DW of the CPU core 2 is stored in a destinationregister synchronously with the rise timing of the clock signal Clock 2at the WB/DSP stage and operations are terminated.

In the case of this example, the destination register is a registerdesignated to Rn. A register which can be designated to Rn is anyregister included in the CPU core 2 (in FIG. 3, any one of the registersA0x, A1x, Ix, A0Y, A1y, and Iy can be designated as Rn). As describedabove, instruction execution is completed at five pipeline stages of IF,ID, EX, MA, and WB/DSP by an instruction for reading data from a memoryto the CPU core 2.

FIG. 9 shows a time chart of an instruction for writing data in a memoryfrom the CPU core 2.

Operations of the instruction are described by taking MOV.L Rm, @Rn asan example of the instruction for writing data from the CPU core 2 intoa memory. Operations of the instruction fetch (IF) and instructiondecode (ID) are the same as those in FIG. 8, detailed description ofthem is omitted.

The data in a register serving as an address pointer is output to theinternal bus A1 of the CPU core 2 synchronously with the rise timing ofthe clock signal Clock 1 at the EX stage. In the case of this example,the register serving as an address pointer serves as a registerdesignated with Rn. A register which can be designated to Rn is anyregister included in the CPU core 2 (in FIG. 3, any one of the registersA0x, A1x, Ix, A0y, A1y, and Iy in Reg. can be designated as Rn). Thedata output to the internal bus A1 of the CPU core 2 is stored in theaddress buffer 205 and output to the address bus IAB synchronously withthe rise timing of the clock signal Clock 2 at the EX stage.

The data output to the internal bus A1 of the CPU core 2 is computed bythe arithmetic and logic unit (ALU) 213. In this case, the arithmeticand logic unit (ALU) 213 performs zero addition arithmetic. Thearithmetic result is output to the internal bus C1 of the CPU core 2.The arithmetic result output to the internal bus C1 of the CPU core 2 isstored in a pointer register (in this case, a register designated withRn) synchronously with the rise timing of the clock signal Clock 2 atthe EX stage.

In the case of the instruction MOV.L Rm, @Rn, address computation isperformed at the EX stage and at the same time, it is prepared to outputthe data to be written in a memory to the data bus IDB. A value isoutput to the internal bus DR of the CPU core 2 from a register storingthe data to be written in the memory synchronously with the rise timingof the clock signal Clock 1 at the EX stage. In the case of thisexample, the register storing the data to be written in the memory is aregister designated with Rm. A register which can be designated with Rmis any register included in the CPU core 2 (in FIG. 3, any one of theregisters A0x, A1x, Ix, A0y, A1y, and Iy in Reg. can be designated asRm). The value output to the internal bus DR of the CPU core 2 is outputto the data bus IDB synchronously with the rise timing of the clocksignal Clock 2 at the MA stage.

In the case of Instruction/Data Mem. Access, an address output to theaddress bus IAB is decoded synchronously with the rise timing of theclock signal Clock 2 at the EX stage in the period between the rise ofthe clock signal Clock 1 and the rise of the clock signal Clock 2 at theMA stage and the data output to the data bus IDB is writtensynchronously with the rise timing of the clock signal Clock.2 at the MAstage and operations are terminated.

In the case of the instruction for writing data from a memory into theCPU core 2, the CPU core 2 terminates operations when outputting data tothe data bus IDB. Therefore, operations are completed at four pipelinestages of IF, ID, EX, and MA.

FIG. 10 shows a time chart for executing a DSP instruction. Operationsof the instruction are described below by taking PADDC Sx, Sy, Dz NOPXNOPY as an example of the DSP instruction. This instruction adds thedata stored in registers in the DSP engine 3 but it does not transferdata between the DSP engine 3 and the X-ROM 4 or X-RAM 6 or between theY-ROM 5 and Y-RAM 7.

Because instruction fetch operation is the same as that in FIG. 7, itsdetailed description is omitted.

At the ID stage, an instruction code captured by the CPU core 2 isdecoded in the period between the clock signal Clock 1 and the clocksignal Clock 2 and the result of decoding the instruction code at thetiming of the clock signal Clock 2 at the ID stage is output to the DSPengine 3 as the DSP control signal 20.

When the DSP engine 3 receives the DSP control signal 20 from the CPUcore 2, it decodes the DSP control signal 20 received up to the periodof the MA stage. A register storing source data is accessedsynchronously with the rise timing of the clock signal Clock 1 at theWB/DSP stage and the value in the register is output to the internalbuses A2 and B2.

In the case of this example, registers storing source data are registersdesignated with Sx and Sy. Registers which can be designated with Sx andSy are any registers in the DSP engine 3 (in FIG. 4, any registers inReg. can be designated as Sx and Sy). The data output to the internalbuses A2 and B2 of the DSP engine 3 is computed by the arithmetic andlogic unit (ALU) 302 and the result is output to the internal bus C2 ofthe DSP engine 3. The arithmetic result output to the internal bus C2 ofthe DSP engine 3 is stored in a destination register synchronously withthe rise timing of the clock signal Clock 2 at the WB/DSP stage. In thecase of this example, the destination register is a register designatedwith Dz. A register which can be designated to Dz is any register in theDSP engine 3 (in FIG. 4, any register in Reg.).

In the case of the above DSP instruction, operations are completed atfive pipeline stages of IF, ID, EX, MA, and WB/DSP.

FIG. 11 shows a time chart of an instruction for reading data from the Xand Y memories 4 to 7 to the DSP engine 3. Operations of the instructionare described below by taking MOVX.W @Ax, Dx MOVY.W @Ay, Dy as anexample of the instruction. This instruction transfers the data storedin addresses designated with Ax and Ay to registers designated with Dxand Dy. Because instruction fetching and instruction decoding are thesame as those in FIG. 10, detailed description of them is omitted.

When executing an instruction for reading data from the X and Y memories4 to 7 to the DSP engine 3, the CPU core 2 generates the address of amemory to be accessed. Therefore, a register storing the address to beaccessed is accessed synchronously with the rise timing of the clocksignal Clock 1 at the EX stage and Values in the register are output tothe internal buses A1 and A2 of the CPU core 2.

In the case of this example, a register storing an address to beaccessed is a register designated with Ax or Ay. A register which can bedesignated to Ax is a register A0x or A1x included in the CPU core 2 anda register which can be designated to Ax is a register A0y or A1yincluded in the CPU core 2. The data output to the internal buses A1 andA2 of the CPU core 2 is stored in the memory address buffers (MABX andMABY) and output to the address buses XAB and YAB synchronously with therise timing of the clock signal Clock 2 at the EX stage.

The ALU 213 and PAU 212 apply address computation to the data output tothe internal buses Al and A2 of the CPU core 2. In this case; the ALU213 and PAU 212 perform zero addition arithmetic. The arithmetic resultsare output to the internal buses C1 and C2 of the CPU core 2. Thearithmetic results output to the internal buses C1 and C2 of the CPUcore 2 are stored in pointer registers (in this case, registersdesignated with Ax and Ay) synchronously with the rise timing of theclock signal Clock 2 at the EX stage.

In the X and Y memories 4 to 7, the addresses output to the addressbuses XAB and YAB are decoded at the rise timing of the EX-stage clocksignal Clock 2 in the period between the rise of the clock signal Clock1 and the rise of the clock signal Clock 2 at the MA stage and data isaccessed in the period between the rise of the clock signal Clock 2 andthe rise of the next clock signal Clock 1 at the MA stage. Therefore,data is output to the data buses XDB and YDB from the time when theclock signal Clock 2 rises at the MA stage.

The data output to the data buses XDB and YDB is captured by the DSPengine 3 synchronously with the rise timing of the clock signal-Clock 1at the WB/DSP stage and supplied to the internal buses D1 and D2 of theDSP engine 3. The data on the internal buses D1 and D2 of the DSP engine3 is stored in destination registers synchronously with the rise timingof the clock signal Clock 2 at the WB/DSP stage and operations areterminated.

In the case of this example, the destination registers are registersdesignated to Dx and Dy. A register which can be designated to Dx is aregister X0 or X1 included in the DSP engine 3 and a register which canbe designated to Dy is a register Y0 or Y1 included in the DSP engine 3.

As described above, in the case of the instruction for reading data froma memory to the DSP engine 3, operations are completed at five pipelinestages of IF, ID, EX, MA, and WB/DSP. This parallel data read can beperformed because the CPU core 2 can access the X and Y memories 4 to 7through the buses XAB and XDB and the buses YAB and YDB which areindependent each other.

FIG. 12 shows a time chart for writing data in the X and Y memories 6and 7 from the DSP engine 3. Operations of an instruction for writingdata in the X and Y memories 6 and 7 from the DSP engine 3 are describedbelow by taking MOVX.W Da, @Ax MOVY.W Da, @AY as an example of theinstruction. This instruction transfers data stored in a registerdesignated with Da to addresses stored in registers designated with Axand Ay.

Because instruction fetching and instruction decoding are the same asthose in FIG. 11, detailed description of them is omitted.

When executing an instruction for writing data in the X and Y memories 6and 7 from the DSP engine 3, the CPU core 2 generates a memory addressto be accessed. Therefore, registers storing addresses to be accessedare accessed synchronously with the rise timing of the clock signalClock 1 at the EX stage and values in the registers are output to theinternal buses A1 and A2 of the CPU core 2. In the case of this example,the registers storing addresses to be accessed are registers designatedwith Ax and Ay. A register which can be designated to Ax is a registerA0x or A1x included in the CPU core 2 and a register which can bedesignated to Ay is a register A0y or A1y included in the CPU core 2.

The data output to the internal buses A1 and A2 of the CPU core 2 isstored in the memory address buffers (MABX and MABY) and output to theaddress buses XAB and YAB synchronously with the rise timing of theclock signal Clock 2 at the EX stage.

An internal register of the DSP engine 3 storing data to be transferredis accessed synchronously with the rise timing of the clock signal Clock1 at the MA stage and values in the register are output to the internalbuses D1 and D2 of the DSP engine 3 and stored in the memory databuffers (MDBX and MDBY). In the case of this example, the internalregister of the DSP engine 3 storing data to be transferred is aregister designated with Da. Registers which can be designated with Daare registers A0 and A1 included in the DSP engine 3.

The data stored in the memory data buffers (MDBX and MDBY) is output tothe data buses XDB and YDB synchronously with the rise timing of theclock signal Clock 2 at the MA stage. In the X and Y memories 6 and 7,addresses output to the address buses XAB and YAB are decoded at therise timing of the EX-stage clock signal Clock 2 in the period betweenthe rise of the clock signal Clock 1 and the rise of the clock signalClock 2 at the MA stage and data is accessed in the period between therise of the clock signal Clock 2 and the rise of the next clock signalClock 1 at the MA stage. Therefore, the data output to the data busesXDB and YDB is written from the time when the clock signal Clock 2 risesat the MA stage.

As described above, in the case of the instruction for writing data inthe X and Y memories 6 and 7 from the DSP engine 3, operations arecompleted at four pipeline stages of IF, ID, EX, and MA. This paralleldata write can be performed because the CPU core 2 can access the X andY memories 4 and 6 through the buses XAB and XDB and the buses TAB andYDB which are independent each other.

FIG. 13 shows a time chart for reading data from a memory to the DSPengine 3.

Operations of an instruction for reading data from a memory to the DSPengine 3 are described below by taking MOVS.L @As, Ds as an example ofthe instruction. This instruction transfers data stored in an addressdesignated with As to a register designated with Ds.

The basic operation is the same as the data read from the X and Ymemories 4 to 7 to the DSP engine 3 shown in FIG. 11. FIGS. 11 and 13are different from each other in that the X and Y buses are used in FIG.11 because purposed memories are the X and Y memories 4 to 7 but thebuses IAB and IDB are used in FIG. 13 because the purposed memory is amemory connected to an address space supported by the microcomputer 1.

The register holding an address to be accessed is accessed synchronouslywith the rise timing of the clock signal Clock 1 at the EX stage and avalue in the register is output to the internal bus Al of the CPU core2. In the case of this example, the register storing an address to beaccessed is a register designated with As. A register which can bedesignated with As is any register in Reg. included in the CPU core 2.The data output to the internal bus A1 of the CPU core 2 is stored inthe address buffer 205 and output to the address bus IAB synchronouslywith the rise timing of the clock signal Clock 2 at the EX stage.

The arithmetic and logic unit (ALU) 213 applies address computation tothe data output to the internal bus A1 of the CPU core 2. In this case,the arithmetic and logic unit (ALU) 213 performs zero additionarithmetic. The arithmetic result is output to the internal bus Cl ofthe CPD core 2.

The arithmetic result output to the internal bus C1 of the CPU core 2 isstored in a pointer register (in this case, a register designated withAs) synchronously with the rise timing of the clock signal Clock 2 atthe EX stage. In the memory to be accessed, the address output to theaddress bus IAB is decoded at the rise timing of the EX-stage clocksignal Clock 2 in the period between the rise of the clock signal Clock1 and the rise of the clock signal Clock 2 at the MA stage and data isaccessed in the period between the rise of the clock signal Clock 2 andthe rise of the next clock signal Clock 1 at the MA stage.

Therefore, data is output to the data bus IDB from the time when theclock signal Clock 2 rises at the MA stage. The data output to the databus IDB is captured by the DSP engine 3 synchronously with the risetiming of the clock signal Clock 1 at the WB/DSP stage and supplied tothe internal bus D1 of the DSP engine 3. The data on the internal bus D1of the DSP engine 3 is stored in a destination register synchronouslywith the rise timing of the clock signal Clock 2 at the WB/DSP stage andoperations are terminated.

In the case of this example, the designation register is a registerdesignated with Ds. A register which can be designated to Ds is anyregister in the DSP engine 3. As described above, in the case of theinstruction for writing data in the DSP engine 3 from a memory,operations are completed at five pipeline stages of IF, ID, EX, MA, andWB/DSP.

FIG. 14 shows a time chart for writing data in a memory from the DSPengine 3.

Operations of an instruction for writing data in a memory from the DSPengine 3 are described below by taking MOVS.L Ds, @As as an example ofthe instruction. This instruction transfers data stored in a registerdesignated with Ds to an address designated with As.

The basic operation is the same as the data write in the X and Ymemories from the DSP engine 3 shown in FIG. 12. FIGS. 12 and 14 aredifferent from each other in that the buses XAB and XDB and the busesYAB and YDB are used in FIG. 12 because purposed memories are the X andY memories but the buses IAB and IDB are used in FIG. 14 because thepurpose memory is a memory connected to an address space supported bythe microcomputer 1.

The register holding a transfer destination address is accessedsynchronously with the rise timing of the clock signal Clock 1 at the EXstage and a value in the register is output to the internal bus A1 ofthe CPU core 2. In the case of this example, the register storing anaddress to be accessed is a register designated with As. A registerwhich can be designated with As is any register in the register Reg.included in the CPU core 2. The data output to the internal bus A1 ofthe CPU core 2 is stored in the address buffer 205 and output to theaddress bus IAB synchronously with the rise timing of the clock signalClock 2 at the EX stage.

The arithmetic and logic unit (ALU) 213 applies address computation tothe data output to the internal bus A1 of the CPU core 2. In this case,the arithmetic and logic unit (ALU) 213 performs zero additionarithmetic. The arithmetic result is output to the internal bus C1 ofthe CPU core 2. The arithmetic result output to the bus C1 of the CPUcore 2 is stored in a pointer register (in this case, a registerdesignated with As) synchronously with the rise timing of the clocksignal Clock 2 at the EX stage.

A value in the register in the DSP engine 3 storing the data to betransferred is output to the internal bus D1 of the DSP engine 3synchronously with the rise timing of the clock signal Clock 1 at the MAstage and stored in the memory data buffer (MDBI). The data stored inthe memory data buffer (MDBI) is output to the data bus IDBsynchronously with the rise timing of the clock signal Clock 2 at the MAstage. In the case of this example, the register in the DSP engine 3storing the data to be transferred is a register designated to Ds. Aregister which can be designated to Ds is any register in the DSP engine3.

In the memory to be access, the address output to the address bus IAB isdecoded at the rise timing of the EX-stage clock signal Clock 2 in theperiod between the rise of the clock signal Clock 1 and the rise of theclock signal Clock 2 at the MA stage and data is accessed in the periodbetween the rise of the clock signal Clock 2 and the rise of the nextclock signal Clock 1 at the MA stage. Therefore, the data output fromthe DSP engine 3 is written in the memory at the rise timing of theclock signal Clock 2 at the MA stage.

As described above, in the case of the instruction for writing data inan external memory from the DSP engine 3, operations are completed atfour pipeline stages of IF, ID, EX, and MA.

Then, operations of a DSP arithmetic instruction are described below bytaking PADD SK, Sy, Du PMUL Se, Sf, Dg MOVX.W @Ax, Dx MOVY.W @Ay, Dy asan example of the instruction and referring to FIG. 15. This instructionadds and multiplies the data stored in registers in the DSP engine 3 andtransfers the data to the DSP engine 3 from the X-ROM 4 and X-RAM 6 orthe Y-ROM 5 and Y-RAM 7. The operations of the instruction are obtainedby combining the operations in FIG. 10 with those in FIG. 11. Becauseinstruction fetching and instruction decoding are the same as those inFIG. 10, detailed description of them is omitted.

To execute an instruction for reading data from the X and Y memories tothe DSP engine 3, the CPU core 2 generates the address of a memory to beaccessed. Therefore, registers holding addresses to be accessed areaccessed synchronously with the rise timing of the clock signal Clock 1at the EX stage and values in the registers are output to the internalbuses A1 and A2 of the CPU core 2.

In the case of this example, registers storing the addresses to beaccessed are registers designated with Ax and Ay. A register which canbe designated with Ax is a register A0x or A1x included in the CPU core2 and a register which can be designated with Ay is a register A0Y orA1y included in the CPU core 2. The data output to the internal buses A1and A2 of the CPU core 2 are stored in the memory address buffers (MABXand MABY) and output to the address buses XAB and YAB synchronously withthe rise timing of the clock signal Clock 2 at the EX stage.

The ALU 213 and PAU 212 apply address computation to the data output tothe internal buses A1 and A2 of the CPU (in this case, the ALU 213 andPAU 212 performs zero addition arithmetic) and the results are output tothe internal buses C1 and C2 of the CPU core 2. The arithmetic resultsoutput to the internal buses C1 and C2 of the CPU core 2 are stored inpointer registers (in this case, registers designated with Ax and Ay)synchronously with the rise timing of the clock signal Clock 2 at the EXstage.

In the X and Y memories, the addresses output to the address buses XABand YAB are decoded at the rise timing of the clock signal Clock 2 atthe EX stage in the period between the rise of the clock signal Clock 1and the rise of the clock signal Clock 2 at the MA stage and data isaccessed in the period between the rise of the clock signal Clock 2 andthe rise of the next clock signal Clock 1 at the MA stage. Therefore,data is output to the data buses XDB and YDB from the time when theclock signal Clock 2 rises at the MA stage.

The data output to the data buses XDB and YDB is captured by the DSPengine 3 at the rise timing of the clock signal Clock 1 at the WB/DSPstage and output to the internal buses D1 and D2 of the DSP engine 3.The data on the internal buses D1 and D2 of the DSP engine 3 is storedin destination registers (Destination Reg.) synchronously with the risetiming of the clock signal Clock 2 at the WB/DSP stage and operationsare terminated.

In the case of this example, the destination registers are registersdesignated to Dx and Dy. A register which can be designated to Dx is X0or X1 in the DSP engine 3 and a register which can be designated to Dyis Y0 or Y1 in the DSP engine 3.

DSP arithmetic operation is performed simultaneously with the above datatransfer. The registers storing source data are accessed synchronouslywith the rise timing of the clock signal Clock 1 at the WB/DSP stage andvalues in the registers are output to the internal buses A1, A2, B1, andB2 of the DSP engine 3. In the case of this example, the registersstoring source data are registers designated with Sx and Sy for ADD(addition) but registers designated with Se and Sf for MUL(multiplication). Registers designated with Sx, Sy, Se, and Sf are anyregisters in the DSP engine 3.

The data output to the internal buses A1 and B1 of the DSP engine 3 ismultiplied by the MAC 304 and the result is output to the internal busC1 of the DSP engine 3. The data output to the internal buses A2 and B2of the DSP engine 3 is added by the ALU 302 and the result is output tothe internal bus C2 of the DSP engine 3.

The arithmetic results output to the internal buses C1 and C2 of the DSPengine 3 are stored in a destination register synchronously with therise timing of the clock signal Clock 2 at the WB/DSP stage. Thedestination register in this example is a register designated with Dufor ADD operation and a register designated with Dg for MUL operation.Registers which can be designated to Du and Dg are any registers in theDSP engine 3.

As described above, in the case of the instruction for adding andmultiplying data stored in registers in the DSP engine 3 andtransferring the data to the DSP engine 3 from the X-ROM 4 and X-RAM 6or the Y-ROM 5 and Y-RAM 7, operations are completed at five pipelinestages of IF, ID, EX, MA, and WB/DSP.

Operations of a DSP arithmetic instruction are described below by takingfour consecutive instructions as the second example of the DSPinstruction and referring to FIG. 16.

Inst 1: PADD A0, M0, A0 PMUL A1, X0, A1 MOVX.W @R4, X1 MOVY.W @R6, Y0

Inst 2: ADD R8, R9

Inst 3: ADD R10, R11

Inst 4: ADD R12, R13

These four instructions realize different operations in the same clockcycle by using the address buses IAB, XAB, and YAB at the same time.Because instruction operations from Inst 1 t Inst 4 are the same asthose in FIGS. 7 and 15, detailed description of them is omitted.

First, instruction fetch of Inst 1 is performed at the IF stage of Inst1. At the time of the ID stage of Inst 1, instruction fetch is performedbecause the IF stage is set for Inst 2.

While address computation for accessing the X and Y memories isperformed at the EX stage of Inst 1, Inst 2 performs instruction decodefor the ID stage and Inst 3 performs instruction fetch for the IF stage.

At the MA stage of Inst 1, addresses computed at the EX stage are outputto the address buses XAB and YAB (the timing for actually outputtingaddresses starts with the rise timing of the clock signal Clock 2 at theEX stage) and data is captured through the data buses XDB and YDB. Inthis case, Inst 2 performs ADD arithmetic between R8 and R9 to completeoperations because of the EX stage and Inst 3 performs instructiondecode because of the ID stage. Moreover, Inst 4 outputs the addressstoring Inst 4 to the address bus IAB because of the IF stage. Thetiming for actually outputting the address to the address bus IAB startswith the rise timing of the clock signal Clock 2 half cycle before theIF stage of Inst 4. This timing is the same as the timing (second halfof the EX stage and the first half of the MA stage) for Inst 1 to outputaddresses to the address buses XAB and YAB.

That is, the address buses XAB and YAB are used for data transfer andthe address bus IAB is used for instruction fetch. Because themicrocomputer 1 includes the internal address buses IAB, XAB, and YABand the internal data buses IDB, XDB, and YDB respectively connected tothe CPU core 2, it can execute different memory access operations in thesame cycle by using the above three types of internal address buses andthree types of internal data buses.

Thereafter, Inst 1 performs DSP arithmetic at the WB/DSP stage andcompletes operations, Inst 2 already completes operations, Inst 3performs ADD arithmetic between R10 and R11 because of the EX stage andcompletes operations, and Inst 4 performs instruction decode because theID stage.

In the next cycle, only the EX stage of Inst 4 is performed and ADDarithmetic between R12 and R23 is performed to complete operations.

This embodiment has the following functions and advantages.

A built-in memory is divided into Y memories 5 and 7 and X memories 4and 6 by considering the multiply and accumulate operation by the DSPengine 3 and the CPU core 2 is made possible to access the Y memories 5and 7 and the X memories 4 and 6 in parallel through the internal busesXAB and XDB and the internal buses YAB and YDB respectively.

Thereby, it is possible to simultaneously transfer two data values tothe DSP engine 3 from the built-in memories 4 to 7. Moreover, becausethe internal buses XAB and XDB and the internal buses YAB and YDB arealso separate from the internal buses IAB and IDB to be interfaced withthe outside, the CPU core 2 is made possible to access an externalmemory in parallel with the access to the X memories 4 and 6 and the Ymemories 5 and 7. Thus, because there are three types of address busesIAB, XAB, and YAB and three types of data buses IDB, XDB, and YDBrespectively connected to the CPU core 2, it is possible to accessdifferent memories in the same clock cycle by using the three types ofinternal address buses and three types of internal data buses.Therefore, even when a program or data is present in an external memory,it is possible to easily correspond to it and accelerate the arithmeticprocessing.

It is possible to further improve the microcomputer operating easinessby constituting each of the X memories 4 and 6 and the Y memories 5 and7 with a RAM and a ROM.

As described above, the built-in memory is divided into the followingtwo types: the X memories 4 and 6 and the Y memories 5 and 7. Each oftwo types of the divided memories is provided with a ROM and a RAM, anda data memory can be separate from a program memory by using the RAM asthe data memory and the ROM as the program memory. Moreover, it ispossible to transfer two data values to the DSP engine 3 in parallel andefficiently perform instruction fetch, data transfer, and arithmetic bythe parallel pipeline processing.

By providing the modulo address output portion 200 for the CPU core 2,it is possible to accelerate address generation for repetitive operationsuch as multiply and accumulate operation in the CPU core 2.

A CPU instruction is assigned to an address space in which 4 high-orderbits of an instruction code are set to “0000” up to “1110”. In the caseof a DSP instruction, 4 high-order bits of an instruction code are allassigned to “1111”. Moreover, an instruction in which 6 high-order bitsof an instruction code are assigned to address spaces of “111100” and“111101” has a 16-bit instruction code even in the case of a DSPinstruction. An instruction in which 6 high-order bits of an instructioncode are set to “111110” has a 32-bit instruction code. No instructionis assigned to an address space in which 6 high-order bits of aninstruction code are set to “111111” and the address space is a vacantarea. Thus, by applying the above rule to assignment of codes to up to32-bit instruction and decoding 6 high-order bits of an instructioncode, it is possible to decide by a decoder with a small logical scalewhether the instruction concerned is a CPU instruction, a 16-bit DSPinstruction, or a 32-bit DSP instruction and therefor, it is unnecessaryto always decode 32 bits at the same time.

As described above by referring to FIG. 17, unprocessed instruction codedata is set to the instruction register 25 after the instruction fetchtiming. In this case, even if an instruction to be executed is any oneof a 16-bit CPU instruction, 16-bit DSP instruction, and 32-bit DSPinstruction, it is possible to supply 16 high-order bits of theinstruction to the first decode circuit 240 without fail.

A code in field A of a 32-bit DSP instruction is set to the high-orderarea UIR of the instruction register 25 and a 16-bit DSP instructionhaving the same format as field A is also set to the high-order areaUIR. Therefore, in any case, the CPU core 2 can perform necessaryaddress arithmetic and selection of a data path necessary for data fetchsimilarly. That is, it is possible to use the decode circuits 240 and241 in common for data fetch to execute a 32-bit DSP instruction anddata fetch to execute a 16-bit DSP instruction and thereby, decrease thelogical scale of the microcomputer 1.

The invention made by the present inventor is concretely described abovein accordance with embodiments. However, the present invention is notrestricted to the embodiments. It is a matter of course that variousmodifications of the present invention are allowed as long as theyfollow the gist of the present invention.

For example, discrimination of a CPU instruction, 16-bit DSPinstruction, and 32-bit DSP instruction is not restricted to the use of6 high-order bits of an instruction but it is possible to change thenumber of high-order bits correspondingly to the number of instructioncodes. Moreover, it is possible to replace the function for shifting 16low-order bits to higher order for an instruction register with anotherfunction. Furthermore, the number of registers and the type of acomputing unit included in a CPU core or DSP engine are not restrictedto the above embodiments but it is possible to properly change them.Furthermore, it is possible to use more than two memories. Furthermore,it is possible to increase the number of address buses and the number ofdata buses to be connected to memories in accordance with the number ofmemories. For example, a Z memory is newly used in addition to X and Ymemories. Then, an address bus ZAB is connected between a CPU and the Zmemory and a data bus ZDB is connected between a DSP engine and the Zmemory. By using the above structure, it is possible not only to capturedata into the DSP engine from the X and Y memories at the time ofmultiply and accumulate operation but also to write the data whosearithmetic is completed before a currently execute instruction in a Zmemory circuit through a Z bus at the same time. Thus, the wholethroughput of a microcomputer is further improved because arithmeticdata can be captured and written in a memory by one instruction. Thepresent invention is the most suitable for use as a built-in unitcontrol microcomputer to be applied to compression/expansion andfiltering of information in a mobile communication unit, servo control,and image processing in a printer.

The following is the brief description of advantages obtained from atypical invention among those disclosed in this application.

That is, a built-in memory is divided into a first memory and a secondmemory by considering the multiply and accumulate operation by a digitalsignal processor and they are made accessible in parallel by a third busand a second bus respectively. Therefore, a central processing unit cansimultaneously transfer two data values to a digital signal processingunit from the built-in memory.

Moreover, because the third and second buses are separate from the firstbus to be interfaced with an external unit, the central processing unitcan access an external memory in parallel with the access to the secondand first memories.

Thus, because there are first to third address buses and first to thirddata, buses respectively connected to the central processing unit, it ispossible to execute different memory access operations in the same cycleby using these three types of internal buses. Therefore, it is possibleto accelerate arithmetic processing easily a correspondingly to the casein which a program or data is present in an external memory.

Moreover, the built-in memory is divided into the first and secondmemories and each divided memory is provided with a ROM and a RAM.Therefore, by using the RAM as a data memory and the ROM as a programmemory, the data memory and the program memory can be separated fromeach other. Thus, it is possible to transfer two data values to thedigital signal processing unit in parallel and moreover, efficientlyperform instruction fetch, data transfer, and arithmetic by parallelpipeline processing.

Therefore, it is possible to accelerate digital signal processing bymounting the central processing unit and the digital signal processingunit on an LSI.

By assigning in instruction code to an instruction in which a CPUinstruction and a DSP instruction are mixed so that it can bediscriminated that the instruction concerned is a CPU instruction, a16-bit DSP instruction, or a 32-bit DSP instruction by decoding part ofthe instruction code, it is possible to decide the type of theinstruction by a decoder with a small logical scale. Therefore, it isunnecessary to always decode 32 bits at the same time. Thus, it ispossible to prevent the physical scale of an LSI from increasing to theutmost when mounting the central processing unit and the digital signalprocessing unit on the LSI.

By using a first-format instruction having a first code area (bit 9 tobit 0 of the 16-bit DSP instruction illustrated in FIG. 18) and asecond-format instruction having not only a second code area (field A ofthe 32-bit DSP instruction illustrated in FIGS. 20 and 21 but also athird code area (field B of the 32-bit DSP instruction illustrated inFIGS. 20 and 21) for specifying the arithmetic processing using thetransferred data specified by the second code area for the digitalsignal processing unit, means for executing the first- and second-formatinstructions respectively can use decode means having a decode logiccommon to the first and second code areas. Therefore, this also makes itpossible to decrease the logical scale if a microcomputer.

What is claimed is:
 1. A single-chip microprocessor comprising: a firstprocessing unit; a second processing unit synchronously operating withthe first processing unit and including a multiplier; first, second andthird address buses coupled to the fist processing unit; first, secondand third data buses coupled to the second processing unit, wherein thefirst and second data buses are coupled to the first processing unit; afirst memory coupled to the first and second address buses and to thefirst and second data buses; and a second memory coupled to the firstand third address buses and the fist and third data buses.
 2. Asingle-chip microprocessor according to claim 1, wherein the firstprocessing unit comprises: a plurality of general purpose registers; anarithmetic and logic unit; a program counter coupled to the firstaddress bus and storing an instruction address; an instruction registercoupled to the first data bus and storing an instruction supplied fromthe first data bus; and an instruction decoder decoding the instructionfetched in the instruction register and providing control signals inresponse to the decoding, wherein at least certain of the controlsignals control the arithmetic and logic unit.
 3. A single-chipmicroprocessor according to claim 2, wherein the first processing unitfixer comprises an address output circuit providing address signals tothe second and third address buses.
 4. A single-chip microprocessoraccording to claim 3, wherein the address output circuit comprises: afirst address buffer coupled to the second address bus; a second addressbuffer coupled to the third address bus; and an arithmetic operationunit operating on address information to be supplied to the first andsecond address buffers.
 5. A single-chip microprocessor according toclaim 2, wherein the second processing unit comprises a decoder circuitcoupled to receive the control signals provided from the instructiondecoder.
 6. A single-chip microprocessor according to claim 5, whereinthe second processing unit further comprises: first, second and thirddata buffer circuits coupled to the first, second and third data buses,respectively; an internal bus coupled to the multiplier and to thefirst, second and third data buffer circuits; a second arithmetic andlogic unit coupled to the internal bus; and registers coupled to theinternal bus.
 7. A single-chip microprocessor according to claim 1,further comprising an external interface coupled to the first addressbus and the first data bus.
 8. A microprocessor on a semiconductorsubstrate comprising: a first processing unit; a second processing unit;first and second address buses coupled to the first processing unit; afirst data bus coupled to the first processing unit and the secondprocessing unit; a second data bus coupled to the first processing unitand the second processing unit; a first memory coupled to the firstaddress bus and the first data bus; and a second memory coupled to thesecond address bus and the second data bus.
 9. A microprocessoraccording to claim 8, wherein the first processing unit comprises anaddress providing circuit providing first and second address signals tothe first and second address buses, respectively, to access the firstand second memories in parallel, and wherein the second processing unitcomprises first and second data buffer circuits to fetch first andsecond data provided from the first and second memories via the firstand second data buses, respectively.
 10. A microprocessor according toclaim 8, wherein the first processing unit comprises: an instructionregister storing an instruction; an instruction decoder decoding theinstruction stored in the instruction register and providing controlsignals in response to the decoding; and an address providing circuitresponsive to the control signals and providing first and second addressto the first and second address buses, respectively, to access the firstand second memories in parallel; wherein the second processing unitcomprises: first and second data buffer circuits to fetch first andsecond data provided from the first and second memories via the firstand second data buses, respectively; and a multiplier and an arithmeticlogic unit operating on the first and second data provided from thefirst and second data buffer circuits.
 11. A microprocessor according toclaim 10, wherein the second processing unit further comprises a decoderresponsive to the control signals from the instruction decoder andproviding internal control signal for controlling the milkier and thearithmetic logic unit.
 12. A single chip processor comprising: first andsecond data buses transferring data; first and second address busestransferring address signals; a first memory coupled to the firstaddress bus and first data bus, respectively; a second memory coupled tothe second address bus and second data bus, respectively; a firstprocessing unit responsive to an execution of one instruction andproviding first and second address signals to the first and secondaddress buses, respectively; and a second processing unit fetching inone bus cycle first and second data which are output from the first andthe second memories responsive to the access by the first and secondaddress signals.
 13. A single chip processor according to claim 12,wherein the first processing unit includes general purpose registerswhich store the first and the second address signals.
 14. A single chipprocessor according to claim 13, wherein the second processing unitcomprises: an internal bus; a multiplier and an arithmetic logic unitcoupled to the internal bus; data registers; a first data buffer circuitcoupled between the internal bus and the fist data bus; and a seconddata buffer circuit coupled between the internal bus and the second databus.
 15. A single chip processor according to claim 12, wherein thefirst processing unit includes an instruction decoder providing controlsignals by decoding an instruction, and wherein the second processingunit includes a decoder circuit coupled to receive the control signalsfrom the instruction decoder and providing internal control signals forcontrolling operations of an internal circuit in the second processingunit.
 16. A single chip processor according to claim 15, wherein thesecond processing unit includes: an internal bus; a multiplier and anarithmetic logic unit coupled to the internal bus; data registerscoupled to the internal bus; a first data buffer circuit coupled betweenthe internal bus and the first data bus; and a second data buffercircuit coupled between the internal bus and the second data bus;wherein operations of the multiplier, the arithmetic logic unit, thedata registers, the first data buffer circuit and the second data buffercircuit are controlled by the internal control signals.
 17. A singlechip processor according to claim 12, wherein the first processing unitcomprises: a plurality of registers storing thee first and the secondaddress signals; an arithmetic and logic operation unit; an instructionregister storing the instruction; an instruction decoder decoding theinstruction stored in the instruction register and providing controlsignals in response to the decoding; and an address providing circuitresponsive to the control signals and providing first and second addresssignals to the first and second address buses, respectively; whereinoperations of the plurality of registers, the arithmetic and logic unitand the address providing circuit are controlled by the control signals.18. A single chip processor according to claim 17, wherein the secondprocessing unit comprises: a decoder circuit coupled to receive thecontrol signals from the instruction decoder and providing internalcontrol signals; an internal bus; a multiplier and a second arithmeticand logic unit coupled to the internal bus; data registers coupled tothe internal bus; a first data buffer circuit coupled between theinternal bus and the first data bus; and a second data buffer circuitcoupled between the internal bus and the second data bus; wherein themultiplier of the second processing unit, the second arithmetic andlogic unit of the second processing unit, the data registers of thesecond processing unit, the first data buffer circuit of the secondprocessing unit and the second data buffer circuit of the secondprocessing unit correspond to the internal circuit and are controlled bythe internal control signals.
 19. In a single-chip microprocessor, amethod comprising the steps of: processing first-type instructions witha first processing unit; processing DSP-type instructions with a secondprocessing unit synchronously operating with the first processing unit,wherein the second processing unit processes at least some DSP-typeinstructions with a multiplier; communicating address information overfirst, second and third address buses with the first processing unit;committing data over first, second and third data buses to the secondprocessing unit and communicating data over the first and second databuses to the first processing unit; wherein a first memory is coupled tothe first and second address buses and to the first and second databuses, and wherein a second memory is coupled to the first and thirdaddress buses and the first and third data buses; and decoding aninstruction received from the first memory and generating controlsignals in response to the decoding, wherein, in response to the controlsignals, the first processing processes the instruction if theinstruction is a first-type instruction and the second processing unitprocesses the instruction if the instruction is a DSP-type instruction.20. The method of claim 19, wherein the second processing unit processesDSP-type instructions of a first size and a second size, herein thefirst size is greater than the second size, the method furthercomprising a step of code converting the decoded instruction if thedecoding determines that the instruction is a DSP-type instruction ofthe first size.
 21. The method of claim 20, wherein the first processingunit processes first-type instructions of the second size.
 22. Themethod of claim 21, wherein the first size is n bits and the second sizeis n/2 bits.
 23. The method of claim 22, wherein n equals
 32. 24. Themethod of claim 19, wherein the first processing unit accesses anexternal memory and the first memory or the second memory in parallel.25. The method of claim 19, wherein tithe first processing unit providesfirst and second address signals to the second and third address buses,respectively, to access the first and second memories in parallel andHerein the second processing unit fetches first and second data providedfrom the first and second memories via the second and third data buses,respectively.
 26. The method of claim 19, wherein the first processingunit provides first and second address signals to the second and thirdaddress buses, respectively, and the second processing unit fetches inone bus cycle first and second data from the first and the secondmemories responsive to the access by the first and second addresssignals.
 27. In a single-chip microprocessor, a method comprising thesteps of processing first-type instructions with a first processingunit; processing DSP-type instructions with a second processing unitsynchronously operating with the first processing unit, wherein thesecond processing unit processes at least some DSP-type instructionswith a multiplier; communicating address information over first andsecond address buses with the first processing unit; communicating dataover first and second data buses to the second processing unit and tothe first processing unit; wherein a first memory is coupled to thefirst address bus and to the first data bus, and wherein a second memoryis coupled to the second address bus and the second data bus; anddecoding an instruction received from the first memory and generatingcontrol signals in response to the decoding, wherein, in response to thecontrol signals, the first processing processes the instruction if theinstruction is a first-type instruction and the second processing unitprocesses the instruction if the instruction is a DSP-type instruction.28. The method of claim 27, wherein the second processing unit processesDSP-type instructions of a first size and a second size, wherein thefirst size is greater than the second size, the method furthercomprising a step of code converting the decoded instruction if thedecoding determines that the instruction is a DSP-type instruction ofthe first size.
 29. The method of claim 28, wherein the first processingunit processes first-type instructions of the second size.
 30. Themethod of claim 29, wherein the first size is n bits and the second sizeis n/2 bits.
 31. The method of claim 30, wherein n equals
 32. 32. Themethod of claim 27, wherein the first processing unit accesses anexternal memory and the first memory or the second memory in parallel.33. The method of claim 27, wherein the first processing unit providesfirst and second address signals to the first and second address buses,respectively, to access the first and second memories in parallel, andwherein the second processing unit fetches first and second dataprovided from the first and second memories via the first and seconddata buses, respectively.
 34. The method of claim 27, wherein the firstprocessing unit provides first and second address signals to the firstand second address buses, respectively, and the second processing unitfetches in one bus cycle first and second data from the first and thesecond memories responsive to the access by the first and second addresssignals.